FIG. 1.   Mature basidiospores of the stalked puffball mushroom, Calostomasp.  

FIG. 2.   Two different stages of fruiting bodies of an edible puffball mushroom, Calostoma sp. 

Introduction

Mature basidiospores of the stalked puffball mushroom, Calostoma sp., are covered with protruding spines (Fig. 1).  The round basidiospores are ornamented with tapered spines, a unique microscopic morphology of some species in this genus. When the basidiosporesare immature, these protruding spines link the basdiospores  with their basidia and networking mycelia in the fertile region (known as the gleba, shown in Fig. 2).  As the spores become mature, they dry and are released from the mycelial mass. The powdery spore dust is discharged through the opening of the fruiting body like ash from a miniature volcano and easily disperses to attach to the surrounding substrate.  The spores provide protection and efficiency in attaching to the substrate.   

When the immature mushroom is cut (far left in Fig. 2), the inner white part—the spore mass or gleba—containing young basidiospores and the mycelial mass which develops within a transparent gelatinous material is seen. The far right (Fig. 2) shows a mature fruiting body with a perforated spore case atop a reticulate stalk.  The natural habitat of these puffballs—low nutrient, sandy soil and decomposed leaves of a dry deciduous forest—is shown in Fig. 3.  This tropical forest type is populated with the major Dipterocarp tree species such as Shorea spp., Dipterocarpus spp. and Hopea spp.  Recent research indicates that Calostoma cinnabarinum sp. is an ectomycorrhizal mushroom (3), a type of fungus which lives in a symbiotic relationship with a plant by forming a sheath around the plant’s root tips. 

Methods

The fruiting bodies of Calostoma sp. were collected from natural ground habitat in a Dipterocarp forest in Thailand in October, 2004. Basidiospores were removed from the inner chamber of a mature mushroom. They were placed on a stub with adhesive tape, vacuum dried, gold coated, and observed by a Jeol scanning electron microscope at 15 kV, 5,000x. The pictures of fruiting bodies in situ were taken by a digital camera, Pentax Optio 330. The diameter of the immature mushroom is 2.5 to 4.0 cm, while the inner part is 1.5 to 3.0 cm. The outer gelatinous layer is 0.5 to 1.0 cm thick. The stalk is hollow, 3.0 to 4.0 cm long and 1.0 to 1.5 cm thick. The diameter of a mature fruiting body is 1.5 to 2.0 cm.  

Discussion

The microscopic morphology of basidiospores reflects the importance of functional morphology for their fertility. The starlike structure protects the basidiospore from unfavorable conditions, helps it to attach to the substrate, and allows it to survive in a suboptimal environment. Besides the basidiospores of puffball mushrooms, such a starlike shape is noticeably found in various taxa: algae, conidia of fungi, corals, planktons, sea stars, sea urchins, and flowering plants.

References

1. Hawksworth, D. L., B. C. Sutton, and G. C. Ainsworth. 1983. Ainsworth and Bisby’s dictionary of fungi. Commonwealth Mycological Institute, Kew, Surrey, England.

2. Lincoff, G. 2004. Field guide to mushrooms. National Audubon Society, New York, NY.

3. Wilson, A. W., E. A. Hobbie, and D. S. Hibbitt. 2007. The ectomycorrhizal status of Calostoma cinnabarinum determined using isotopic, molecular and morphological methods. Can. J. Bot. 85(4):385–393.